WO2018110660A1 - Particulate matter detection apparatus - Google Patents

Abstract

The present invention is provided with a sensor unit (1) for outputting a signal corresponding to an amount of particulate matter, and a sensor control unit (4) for detecting a particle count (N) of the particulate matter. The sensor control unit has: a collection control unit (41) for applying a first voltage to a pair of electrodes (21), (22) and causing particulate matter to be electrostatically collected; and a particle count calculation unit (42) for detecting a resistance value (R) between the pair of electrodes after a change to a second voltage different from the first voltage is made in a state in which the sensor output at the first voltage has reached a threshold value, and calculating the particle count using the average particle diameter of the particulate matter estimated from the resistance value and the mass (M) of the particulate matter estimated from the sensor output.

Description

Particulate matter detector Cross-reference of related applications

This application is based on Patent Application No. 2016-243417 filed on December 15, 2016 and Patent Application No. 2017-238902 filed on December 13, 2017. The contents of are hereby incorporated by reference.

The present disclosure relates to a particulate matter detection device for detecting the number of particulate matter discharged from an internal combustion engine.

Particulate matter contained in automobile exhaust gas (that is, Particulate Matter; hereinafter referred to as PM as appropriate) is mainly composed of conductive soot (that is, soot), and SOF derived from unburned fuel or engine oil ( That is, it is a mixture containing Soluble Organic Fraction (soluble organic component). The particulate matter detection device includes, for example, an electric resistance type sensor element, applies a voltage to the detection electrode portion provided on the surface of the insulating substrate to form an electrostatic field, and collects particulate matter. The change in the resistance value of the detection electrode portion due to the is detected.

In recent years, emission regulations have become stricter, and it is important to improve the detection accuracy of particulate matter detection devices. In general, in particulate matter detection devices, the amount of particulate matter discharged is estimated from the output of a sensor element, and further, regulation of the amount of particulate matter to be discharged is being studied. For example, Patent Document 1 discloses a sensor control device in which a plurality of electric resistance type PM detection units are arranged and the particulate matter adhering to each PM detection unit is set to have a different particle size distribution. . In this apparatus, the average particle mass per PM is set for each PM detection unit, and the number of PM particles is calculated using the PM mass detected from the sensor output of each PM detection unit and the set average particle mass. .

JP 2012-52811 A

In the apparatus of Patent Literature 1, the average particle mass is set by adjusting the applied voltage to each PM detection unit and utilizing the fact that the particle size range of the particulate matter that adheres increases as the applied voltage increases, The number of PM particles in the particle size range can be calculated. By the way, the state of the particulate matter discharged together with the exhaust gas varies greatly depending on the engine operating conditions. Therefore, for example, if a deviation occurs between the particle diameter of the particulate matter deposited on each PM detection unit and the set particle diameter, there is a problem that the detection accuracy of the number of PM particles calculated thereby also decreases. In addition, since a plurality of PM detection units are used, a problem has been found that the apparatus configuration is complicated, and it is likely to increase the size and cost.

An object of the present disclosure is to provide a particulate matter detection device that improves the detection accuracy of particulate matter by calculating the number of particles by reflecting changes in the particle size of the particulate matter depending on engine operating conditions. To do.

One aspect of the present disclosure is:
A particulate matter detection device for detecting particulate matter contained in a gas to be measured,
A sensor unit having a detection unit in which a pair of electrodes spaced apart from each other are arranged on the surface of the substrate exposed to the gas to be measured, and outputting a signal corresponding to the amount of particulate matter electrostatically collected by the detection unit When,
A sensor control unit that detects the number of particles of the particulate matter electrostatically collected by the detection unit based on a sensor output transmitted from the sensor unit;
The sensor control unit
A collection control unit that applies a first voltage between the pair of electrodes of the detection unit and causes the detection unit to electrostatically collect particulate matter;
The resistance value between the pair of electrodes is detected after changing the applied voltage between the pair of electrodes to a second voltage different from the first voltage in a state where the sensor output at the first voltage has reached a threshold value. A particle number calculating unit that calculates the number of particles using an average particle diameter of the particulate substance estimated from the resistance value and a mass of the particulate substance estimated from the sensor output. It is in the particulate matter detection device.

Another aspect of the present disclosure is a particulate matter detection device that detects particulate matter contained in a gas to be measured.
A sensor unit having a detection unit in which a pair of electrodes spaced apart from each other are arranged on the surface of the substrate exposed to the gas to be measured, and outputting a signal corresponding to the amount of particulate matter electrostatically collected by the detection unit When,
A sensor control unit that detects the number of particles of the particulate matter electrostatically collected by the detection unit based on a sensor output transmitted from the sensor unit;
The sensor control unit
A collection control unit that applies a first voltage between the pair of electrodes of the detection unit and causes the detection unit to electrostatically collect particulate matter;
In a state where the sensor output at the first voltage reaches a threshold value, the voltage applied between the pair of electrodes is changed to a second voltage different from the first voltage, and then the pair at a plurality of voltages having different magnitudes. The number of particles for detecting the resistance value between the electrodes and calculating the number of particles using the average particle size of the particulate matter estimated from the resistance value and the mass of the particulate matter estimated from the sensor output A particulate matter detection device having a calculation unit.

Still another aspect of the present disclosure is a particulate matter detection device that detects particulate matter contained in a gas to be measured.
A sensor unit having a detection unit in which a pair of electrodes spaced apart from each other are arranged on the surface of the substrate exposed to the gas to be measured, and outputting a signal corresponding to the amount of particulate matter electrostatically collected by the detection unit When,
A sensor control unit that detects the number of particles of the particulate matter electrostatically collected by the detection unit based on a sensor output transmitted from the sensor unit;
The sensor control unit
A collection control unit that applies a first voltage between the pair of electrodes of the detection unit and causes the detection unit to electrostatically collect particulate matter;
In a state where the sensor output at the first voltage reaches a threshold value, the voltage applied between the pair of electrodes is changed to a second voltage different from the first voltage, and then the pair at a plurality of voltages having different magnitudes. The resistance value between the electrodes is detected, and the average particle diameter of the particulate matter estimated from the slope in the relationship between the plurality of voltages and the resistance value and the mass of the particulate matter estimated from the sensor output are used. And a particle number calculating unit for calculating the number of particles.

Still another aspect of the present disclosure is a particulate matter detection device that detects particulate matter contained in a gas to be measured.
A sensor unit having a detection unit in which a pair of electrodes spaced apart from each other are arranged on the surface of the substrate exposed to the gas to be measured, and outputting a signal corresponding to the amount of particulate matter electrostatically collected by the detection unit When,
A sensor control unit that detects the number of particles of the particulate matter electrostatically collected by the detection unit based on a sensor output transmitted from the sensor unit;
The sensor control unit
A collection control unit that applies a first current between the pair of electrodes of the detection unit and electrostatically collects particulate matter in the detection unit;
The resistance value between the pair of electrodes is detected after the applied current between the pair of electrodes is changed to a second current different from the first current with the sensor output at the first current reaching a threshold value. A particle number calculating unit that calculates the number of particles using an average particle diameter of the particulate substance estimated from the resistance value and a mass of the particulate substance estimated from the sensor output. It is in the particulate matter detection device.

In the particulate matter detection device according to the aspect, the sensor control unit activates the collection control unit to start electrostatic collection of the particulate matter. When the sensor output reaches the threshold value, the voltage control unit is operated to change the first voltage for collection from the first voltage to the second voltage, and after changing the collection state, the resistance value between the pair of electrodes is detected. To do. At this time, it has been found that there is a correlation between the resistance value between the pair of electrodes and the average particle diameter of the particulate matter, and the detected resistance value increases as the average particle diameter increases. Using this relationship, the average particle diameter of the particulate matter can be estimated from the detected resistance value. Furthermore, the number of particles can be calculated by the particle number calculation unit using the mass of the particulate matter estimated from the sensor output.
Like the said other aspect, after changing to the 2nd voltage different from a 1st voltage, the resistance value in each voltage can also be detected in several voltages. In that case, the average particle diameter of the particulate matter can be estimated using resistance values at a plurality of voltages. Or the average particle diameter of a particulate matter can also be estimated using the inclination in the relationship between a some voltage and resistance value like the said further another aspect. Alternatively, as in the above other embodiment, instead of the first voltage and the second voltage, the first current and the second current may be applied between the pair of electrodes, and the average particle size of the particulate matter may be reduced. Can be estimated.

As described above, according to the above aspect, the number of particles can be calculated by reflecting the change in the particle size of the particulate matter depending on the engine operating conditions, and the particulate matter detection with improved detection accuracy of the particulate matter. An apparatus can be provided.

The above and other objects, features, and advantages of the present disclosure will become more apparent from the following detailed description with reference to the accompanying drawings. The drawing
FIG. 1 is an enlarged view of a main part showing an example of a particulate matter detection sensor constituting a particulate matter detection device in Embodiment 1. FIG. 2 is an overall perspective view showing a configuration example of a sensor element of the particulate matter detection sensor in Embodiment 1. FIG. 3 is a schematic configuration diagram illustrating an overall configuration of an exhaust gas purification apparatus for an internal combustion engine including the particulate matter detection device according to the first embodiment. FIG. 4 is a diagram illustrating an example of sensor output characteristics of the particulate matter detection sensor according to the first embodiment. FIG. 5 is an enlarged view of a main part showing another example of the particulate matter detection sensor according to the first embodiment. FIG. 6 is an overall perspective view illustrating another configuration example of the sensor element of the particulate matter detection sensor according to the first embodiment. FIG. 7 is a flowchart of particulate matter detection processing executed by the sensor control unit of the particulate matter detection device according to the first embodiment. FIG. 8 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the detection time in Embodiment 1. FIG. 9 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the interelectrode resistance in the first embodiment. FIG. 10 is an overall schematic configuration diagram of a model exhaust gas purification apparatus used for examining the relationship between the voltage applied to the detection unit of the sensor element and the interelectrode resistance in the first embodiment. FIG. 11 is a diagram illustrating the relationship between the average particle diameter of the particulate matter collected by the detection unit of the sensor element and the interelectrode resistance in Embodiment 1. FIG. 12 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the slope of a straight line indicating the relationship between the average particle diameter of the particulate matter and the interelectrode resistance in the first embodiment. FIG. 13 is a diagram showing the relationship between the reciprocal of the average particle diameter of the collected particulate matter and the interelectrode resistance in Embodiment 1. FIG. 14 is a schematic diagram for explaining changes in interelectrode resistance depending on the average particle size of the particulate matter and the applied voltage in Embodiment 1. FIG. 15 is a diagram illustrating the relationship between the estimated number of particulate substances and the actually measured number of particulate substances in Embodiment 1. FIG. 16 is a flowchart of particulate matter detection processing executed by the sensor control unit of the particulate matter detection device in Embodiment 2. FIG. 17 is a diagram illustrating an example of the relationship between the number of particles of particulate matter estimated under the condition that there is one detection voltage and the number of particles of actually measured particulate matter in the second embodiment. FIG. 18 is a diagram illustrating an example of the relationship between the number of particles of particulate matter estimated under the condition that there are a plurality of detection voltages and the number of particles of actually measured particulate matter in Embodiment 2. FIG. 19 is a flowchart of particulate matter detection processing executed by the sensor control unit of the particulate matter detection device in Embodiment 3. FIG. 20 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the interelectrode resistance in the third embodiment. FIG. 21 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the interelectrode resistance in the third embodiment. FIG. 22 is a diagram showing the relationship between the reciprocal of the average particle diameter of the collected particulate matter and the interelectrode resistance in Embodiment 3. FIG. 23 is a diagram showing the relationship between the reciprocal of the average particle diameter of the collected particulate matter and the slope of the relational expression between applied voltage and interelectrode resistance in Embodiment 3. FIG. 24 is a flowchart of particulate matter detection processing executed by the sensor control unit of the particulate matter detection device in Embodiment 4. FIG. 25 is a diagram showing a change in element temperature during heat treatment of the sensor element in the fourth embodiment. FIG. 26 is a diagram showing the relationship between the presence / absence of heat treatment of the sensor element, the reciprocal of the average particle diameter of the particulate matter, and the interelectrode resistance in Embodiment 4. FIG. 27 is a flowchart of particulate matter detection processing executed by the sensor control unit of the particulate matter detection device according to the fifth embodiment. FIG. 28 is an overall view showing a configuration example of a sensor element of a particulate matter detection sensor in Embodiment 6. FIG. 29 is a cross-sectional view illustrating a configuration example of the detection unit of the sensor element in the sixth embodiment, and is a cross-sectional view taken along the line AA in FIG. FIG. 30 is a graph showing the relationship between the surface electrical resistivity and the temperature of the high-resistance conductive material constituting the detection unit of the sensor element in Embodiment 6. FIG. 31 is a diagram for explaining a method of measuring the surface electrical resistivity in the sixth embodiment. FIG. 32 is a diagram for explaining a method for measuring bulk electrical resistivity in the sixth embodiment. FIG. 33 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the interelectrode resistance in the sixth embodiment. FIG. 34 is a diagram showing the relationship between the reciprocal of the average particle diameter of the collected particulate matter and the interelectrode resistance in Embodiment 6. FIG. 35 is an enlarged cross-sectional view schematically showing an initial state in which particulate matter is not deposited on the detection part of the sensor element in the sixth embodiment. FIG. 36 is an enlarged cross-sectional view schematically showing a state in which particulate matter adheres to the detection part of the sensor element in the sixth embodiment. FIG. 37 is a diagram illustrating the relationship between the amount of particulate matter deposited on the detection unit of the sensor element and the sensor output in the sixth embodiment. FIG. 38 is a diagram illustrating an example of the relationship between the estimated number of particulate matter particles and the actually measured number of particulate matter particles in Embodiment 6. FIG. 39 is a flowchart of the particulate matter detection process executed by the sensor control unit of the particulate matter detection device according to the seventh embodiment. FIG. 40 is a diagram showing the relationship between the average particle size and specific gravity of particulate matter in Embodiment 7. FIG. 41 is a diagram illustrating an example of the relationship between the estimated number of particles of particulate matter and the actually measured number of particles of particulate matter in the embodiment 7. FIG. 42 is a diagram illustrating an example of the relationship between the estimated number of particulate substances and the actually measured number of particulate substances in Embodiment 7. FIG. 43 is a flowchart of particulate matter detection processing executed by the sensor control unit of the particulate matter detection device in Embodiment 8. FIG. 44 is a diagram showing the relationship between the average particle size of the collected particulate matter and the interelectrode resistance in Embodiment 8. FIG. 45 is a diagram illustrating an example of the relationship between the estimated number of particulate matter particles and the actually measured number of particulate matter particles in Embodiment 8. FIG. 46 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the interelectrode resistance in the eighth embodiment. FIG. 47 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the measurement current in the eighth embodiment; FIG. 48 is a diagram illustrating the relationship between the voltage applied to the detection unit of the sensor element and the amount of change in resistance between the electrodes in the eighth embodiment. FIG. 49 is a diagram showing the relationship between the average particle size of collected particulate matter and the resistance change between electrodes in Embodiment 8. FIG. 50 is a diagram showing the relationship between the average particle diameter of the particulate matter to be collected and the resistance change amount between the electrodes in Embodiment 8. FIG. 51 is a diagram showing the relationship between the average particle diameter of the collected particulate matter and the interelectrode resistance in the eighth embodiment.

(Embodiment 1)
Next, an embodiment of the particulate matter detection device will be described with reference to the drawings. As shown in FIGS. 1 to 3, the particulate matter detection device detects particulate matter contained in the gas G to be measured, and includes a particulate matter detection sensor 1 as a sensor unit, and particulate matter detection. An electronic control unit (hereinafter referred to as an ECU) 4 is provided as a sensor control unit that detects the number of particles of the collected particulate matter based on the sensor output from the sensor 1.
The ECU 4 includes a collection control unit 41, a particle number calculation unit 42, and a heating control unit 43. The ECU 4 outputs a control signal to the particulate matter detection sensor 1 or receives a detection signal to capture the particulate matter. Control collection and detection. The particle number calculation unit 42 includes a voltage control unit 421 and an interelectrode resistance detection unit 422. Details of these parts will be described later.

As shown in FIG. 1, the particulate matter detection sensor 1 includes an electric resistance type sensor element 10 and a protective cover 12 covering the outer periphery thereof. The sensor element 10 is detected by being exposed to the gas G to be measured on the front end side (that is, the lower end side in FIG. 1) with the axial direction of the protective cover 12 as the longitudinal direction X (that is, the vertical direction in FIG. 1). Part 2 is provided. The detection unit 2 can be heated by a heater unit 3 built in the sensor element 10. The protective cover 12 has a cylindrical body shape made of a metal material such as stainless steel, and has a plurality of measured gas flow holes 13 and 14 on the side surface and the front end surface. For example, as shown in the drawing, the gas to be measured is introduced into the protective cover 12 from the gas flow hole 13 to be measured on the side surface facing the detection unit 2, and the gas to be measured on the tip surface along the surface of the detection unit 2. A flow of the gas to be measured G toward the flow hole 14 is formed.

As shown in FIG. 2, the sensor element 10 has a rectangular parallelepiped-shaped insulating base 11 as a base, and the front end side in the longitudinal direction X of the insulating base 11 (that is, the right end side in the left-right direction in FIG. 2). It has a detection unit 2 to be formed and a heater unit 3 embedded in the insulating substrate 11. The detection unit 2 includes a pair of electrodes 21 and 22 that are printed in a comb shape on one side surface of the insulating substrate 11 (that is, the upper side surface in FIG. 2 and the left side surface in FIG. 1). The comb- like electrodes 21 and 22 are each composed of a plurality of linear electrodes, and linear electrodes having different polarities are alternately arranged in parallel to constitute a plurality of electrode pairs. The electrodes 21 and 22 are respectively connected to linear lead electrodes 21a and 22a extending from the distal end side of the insulating base 11 to the proximal end side (that is, the left end side in FIG. 2).

The heater unit 3 includes a heater electrode 31 disposed on the distal end side of the insulating substrate 11 and lead electrodes 31a and 31b connected to the heater electrode 31 and extending to the proximal end side. The insulative base 11 is constituted by a laminated body of a plurality of insulative sheets made of an insulative ceramic material such as alumina, for example. At this time, the heater electrode 31 and the lead electrodes 31a and 31b are printed on the surface of the insulating sheet, and the other insulating sheets are overlapped to form a predetermined rectangular parallelepiped shaped body, which is fired. Thereby, the sensor element 10 which incorporates the heater part 3 can be formed.

The electrodes 21 and 22 of the detection unit 2, the lead electrodes 21 a and 22 a, the heater electrode 31 of the heater unit 3, and the lead electrodes 31 a and 31 b are made of a conductive material such as a noble metal, for example, and are predetermined electrodes using screen printing or the like. It can be formed into a shape. In addition, the heater part 3 is not embedded in the insulating base | substrate 11, but the heater part 3 can also be printed and formed on the surface of the insulating base | substrate 11, for example, the side surface different from the one side surface in which the detection part 2 is formed. The heater unit 3 only needs to be configured to be able to heat the detection unit 2, and can be provided separately from the insulating substrate 11, for example.

A predetermined voltage is applied from the ECU 4 to the electrodes 21 and 22 of the detection unit 2 via the lead electrodes 21a and 22a, respectively. That is, when the collection control unit 41 is operated, the first voltage is applied between the pair of electrodes 21 and 22, and the sensor output V corresponding to the amount of particulate matter electrostatically collected is acquired. In addition, when the particle number calculation unit 42 is activated, a second voltage is applied from the voltage control unit 421, and the resistance value between the electrodes 21 and 22 at the second voltage (hereinafter, appropriately between the electrodes) is detected by the interelectrode resistance detection unit 422. R) (referred to as resistance) is measured.

The gas to be measured G is, for example, combustion exhaust gas discharged from the internal combustion engine E shown in FIG. 3, and the particulate matter (that is, PM) is soot (that is, soot) that is a conductive component and an organic component. A mixture containing SOF (ie, soluble organic components). The discharge amount of particulate matter and the state of particles, for example, the particle size and chemical composition vary depending on the operating state of the internal combustion engine E. The internal combustion engine E is, for example, a diesel engine, and a diesel particulate filter (hereinafter referred to as a DPF) 5 serving as a particulate matter collecting unit is disposed in an exhaust gas passage E1 through which exhaust gas flows. The particulate matter detection sensor 1 is disposed downstream of the DPF 5 and is fixedly attached to the wall of the exhaust gas passage E1 so that the tip half is located in the exhaust gas passage E1. The particulate matter detection sensor 1 is connected to the ECU 4 and outputs a detection signal corresponding to the amount of PM in the exhaust gas downstream of the DPF 5 to the ECU 4.

The ECU 4 controls the operation of the detection unit 2 and the heater unit 3 of the particulate matter detection sensor 1 and controls the operating state of the internal combustion engine E. In FIG. 3, an exhaust gas temperature sensor 51 is attached and fixed to the wall of the exhaust gas passage E1 in the vicinity of the particulate matter detection sensor 1 so that the exhaust gas temperature downstream of the DPF 5 can be detected. An air flow meter 52 is provided to detect the intake flow rate. Further, a rotation speed sensor 53 for detecting the rotation speed of the internal combustion engine E, an accelerator pedal sensor 54 for detecting the operation of the accelerator pedal, and other various detection devices are provided. Detection signals from these various detection devices are input to the ECU 4.

ECU4 is a well-known structure provided with the microcomputer 4A, and is connected to various detection apparatuses via the input / output interface I / F. The microcomputer 4A includes a CPU that performs arithmetic processing, a ROM that stores programs and data, and a RAM. The microcomputer 4A periodically executes the program to control each part of the internal combustion engine E including the particulate matter detection sensor 1. To do. For example, the ECU 4 executes a particulate matter detection process based on a prestored program, outputs a control signal to the particulate matter detection sensor 1, deposits the particulate matter on the detection unit 2 of the sensor element 10, and Based on the output signal transmitted from the element 10, the particulate matter electrostatically collected by the detection unit 2 is detected.

Here, depending on the operating conditions of the internal combustion engine E, the particle diameter of the particulate matter discharged into the exhaust gas passage E1 varies. When the particle size of the discharged particulate matter changes, the conductivity changes, so the resistance of the particulate matter collected by the detection unit 2 changes, and even if the collected amount is the same with the same chemical composition It has been found that the sensor output V is different. Therefore, in this embodiment, the change in the resistance value between the pair of electrodes 21 and 22 accompanying the change in the average particle diameter is grasped in advance, so that the particle diameter of the particulate matter is estimated and the number of particles is accurately calculated. .

Specifically, as shown in FIG. 1, the ECU 4 applies a first voltage between the pair of electrodes 21 and 22 of the detection unit 2 to form an electrostatic field, and generates particulate matter in the gas G to be measured. A collection control unit 41 that electrostatically collects and a particle number calculation unit 42 that calculates the number N of particles of the collected particulate matter are provided. The particle number calculation unit 42 detects the resistance value R between the pair of electrodes 21 and 22 after changing to the second voltage different from the first voltage in a state where the sensor output V at the first voltage reaches the threshold value. Then, the number N of particles is calculated using the average particle diameter D of the particulate matter estimated from the detected resistance value R and the mass M of the particulate matter estimated from the sensor output V.

More specifically, the particle number calculation unit 42 determines the voltage applied between the pair of electrodes 21 and 22 at the time when the sensor output V at the first voltage for electrostatic collection reaches a threshold value. After changing to the second voltage for changing the collection state of the substance, between the voltage control unit 421 that controls to the detection voltage and the resistance value R between the pair of electrodes 21 and 22 in the detection voltage A resistance detection unit 422. The detection voltage is the same voltage as or different from the second voltage, and is a voltage for detecting the interelectrode resistance.

As shown in FIG. 4, the output characteristic of the particulate matter detection sensor 1 (for example, shown here as a current-time characteristic) is a dead period in which the sensor output becomes zero for a certain period after the start of collection. Thereafter, when the pair of electrodes 21 and 22 are electrically connected by the collected particulate matter, the sensor output starts to increase, and the sensor output increases as the deposition amount increases. Particulate matter can be detected after this output value reaches a preset threshold value (ie, detection time t in FIG. 4).

In the voltage control unit 421, the first voltage is set so that electrostatic collection of the particulate matter by the collection control unit 41 is promoted and the sensor output V rises quickly. As a result, when the particulate matter is discharged, the threshold value can be reached quickly, and then the process can proceed to the calculation of the particle number N by the particle number calculation unit 42.
On the other hand, the second voltage is set so that the collection state of the particulate matter at the time when the threshold value is reached, for example, the contact resistance and the contact state of the collected particulate matter are changed. The second voltage can be set to any voltage different from the first voltage, and may be higher or lower than the first voltage. By changing the applied voltage, the collected state of the collected particulate matter changes according to the particle size, so that the resistance value R according to the particle size can be detected in the interelectrode resistance detection unit 422. .

Further, the detection voltage is set to a voltage that makes it easy to determine the change in the resistance value R according to the particle diameter. The detection voltage can be set to any voltage suitable for detecting the resistance value R, and may be the same voltage as the first voltage or the second voltage.
Preferably, the second voltage has a larger voltage difference with respect to the first voltage, and the change in the collection state becomes larger. The detection voltage may be set so that the voltage difference from the first voltage is larger within a range in which the resistance value R can be detected with high sensitivity.

Generally, when the applied voltage is changed to a voltage lower than the first voltage, the resistance value R between the pair of electrodes 21 and 22 tends to increase, and the tendency increases as the particle diameter increases. . Therefore, for example, the voltage lower than the first voltage can be set as the second voltage to change the collection state of the particulate matter, and further, the resistance value R can be detected using the second voltage as the detection voltage. Then, the average particle diameter D can be estimated from the resistance value R detected at the second voltage and the relational expression between the prepared resistance value R and the average particle diameter D of the particulate matter.

Therefore, by appropriately setting the first voltage and the second voltage (for example, detection voltage = second voltage), the resistance value R is detected with high sensitivity, and the average particle diameter D is accurately estimated from the resistance value R. Is possible. Then, the mass M of the particulate matter can be known from the sensor output V, and the average particle diameter D estimated from the resistance value R can be used to accurately calculate the number N of particles.

Further, the ECU 4 includes a heating control unit 43 that supplies power to the heater electrode 31 of the heater unit 3 to heat the detection unit 2 to a predetermined temperature. The heating control unit 43 can, for example, operate the heater unit 3 prior to the collection and detection of the particulate matter and burn and remove the particulate matter deposited on the detection unit 2. Thereby, the particulate matter detection sensor 1 can be regenerated.

As shown in FIGS. 5 and 6, the sensor element 10 of the particulate matter detection sensor 1 is configured to have a detection unit 2 including a pair of electrodes 21 and 22 having a laminated structure on the distal end surface of an insulating substrate 11. Also good. The sensor element 10 is formed, for example, by firing a laminate in which electrode films to be the electrodes 21 or 22 are alternately arranged between a plurality of insulating sheets to be the insulating base 11. At this time, the edge portions of the electrode films to be the electrodes 21 and 22 are alternately exposed on the front end surface of the insulating substrate 11 to form a plurality of electrode pairs composed of linear electrodes having different polarities. The electrode films to be the electrodes 21 or 22 are connected to lead electrodes (not shown), and are connected to each other on the base end side of the insulating substrate 11.

In the protective cover 12, the sensor element 10 having the detection unit 2 having a laminated structure has a distal end surface slightly located at the distal end surface where the detection unit 2 is located than the plurality of gas flow holes 13 to be measured opened on the side surface of the protective cover 12. It is arranged to be located on the side. The configuration of the protective cover 12 is the same as that of the example shown in FIG. 1, and the measured gas G flows into the protective cover 12 from the plurality of measured gas flow holes 13 on the side surface, and the measured gas flow on the front end surface. The gas flows toward the hole 14. At this time, the flow of the gas to be measured G does not go directly from the gas to be measured flow hole 13 to the detection unit 2, and the flow of the gas to be measured G introduced into the protective cover 12 is in the vicinity of the front end surface of the sensor element 10. The gas flows toward the gas flow hole 14 to be measured on the front end surface.

The sensor element 10 is also provided with a heater unit 3 (not shown), and the heater electrode 31 and its lead electrodes 31a and 31b are embedded in the insulating base 11 or printed on the surface of the insulating base 11. Can do. In the sensor element 10 having a laminated structure, the detection unit 2 may be disposed on one side surface of the distal end side without being formed on the distal end surface. Also in this case, the configuration in which the insulating films to be the electrodes 21 and 22 are arranged between the insulating sheets to be the insulating base 11 and the thickness of the insulating sheet is the distance between the electrodes 21 and 22 is the same.

Such a particulate matter detection device can be used for failure diagnosis of the DPF 5 arranged upstream of the particulate matter detection sensor 1 in FIG. In general, if the DPF 5 is normal, the discharged particulate matter is collected by the DPF 5 and hardly discharged downstream. When the particulate matter collection performance is reduced due to some abnormality in the DPF 5, the particulate matter detection sensor 1 on the downstream side measures the number N of the particulate matter to be discharged. Presence / absence can be determined. At that time, the detection variation due to the influence of the particle size of the particulate matter is reduced, so that the detection accuracy of the particulate matter detection sensor 1 can be improved and the abnormality can be detected promptly.

Below, the detail of the particulate matter detection process performed by ECU4 is demonstrated using a flowchart. As shown in FIG. 7, the present embodiment is an example in which the second voltage and the detection voltage are the same voltage, and the second voltage is lower than the first voltage.
In FIG. 7, when the particulate matter detection process is started, the particulate matter is collected in the detection unit 2 of the particulate matter detection sensor 1 in step S1. At the start of collection, it is assumed that the particulate matter is burned and removed in advance by the regeneration process of the particulate matter detection sensor 1 performed in a separate routine, and the particulate matter is not deposited on the detection unit 2. The regeneration process is performed by energizing the heater unit 3 built in the sensor element 10 and heating the detection electrode unit 2. The temperature of the detection unit 2 at the time of regeneration is normally set to 600 ° C. or higher at which the Soot can be burned and removed.

Step S <b> 1 is a process as the collection control unit 41 of the ECU 4, and a preset first voltage is applied between the pair of electrodes 21 and 22 of the sensor element 10 and is introduced into the protective cover 12. Particulate matter is deposited on the detector 2. In the detection unit 2, the particulate matter detection sensor 1 captures the particulate matter between the pair of electrodes 21 and 22, and detects an electrical characteristic that changes depending on the amount of the particulate matter. As described above, the particulate matter detection sensor 1 preferably has the sensor output V quickly reaching the threshold value.

Therefore, the collection control unit 41 selects the first voltage applied between the pair of electrodes 21 and 22 so that the detection time of the sensor output V is minimized. The threshold is, for example, a predetermined output serving as a detection reference for failure diagnosis of the DPF 5, and can be set to an output value V0 corresponding to the minimum amount of particulate matter that can be detected. In the stacked sensor element 10, the distance between the pair of electrodes 21 and 22 (that is, the electrode interval) is set, for example, in the range of 5 μm to 100 μm. In general, the detection sensitivity increases as the distance decreases.

As shown in FIG. 8, when the flow rate of the exhaust gas is constant (for example, 11.4 m / s), the detection time is relatively long in the region where the applied voltage is low, and the detection time decreases as the applied voltage increases, For example, the detection time is shortest when the applied voltage is in the vicinity of 30V to 40V. As the applied voltage becomes higher, the detection time increases again. Therefore, the sensor output V can be quickly raised by setting the first voltage within a range of 30 V to 40 V (for example, 35 V) that minimizes the detection time.

This is considered because the electric adhesion force P of the particulate matter to the detection unit 2 depends on the Coulomb force and the repulsive force as represented by the following formula 1.
Formula ^{1: PαD 2 (KEIρ1-E} 2/32)
However,
D: Average particle diameter K: Coefficient E: Electric field strength I: Corona current ρ1: Particle electrical resistivity In the above equation 1, the first term in parentheses represents the Coulomb force, and the second term represents the repulsive force. That is, in the low applied voltage region, the Coulomb force is dominant and the detection time is reduced, and in the high applied voltage region, the repulsive force is dominant and the detection time is increased. In this way, the electric adhesion force P is determined by the balance between the Coulomb force and the repulsive force, and there is an optimum value of the applied voltage that minimizes the detection time because the Coulomb force is relatively large and the repulsive force is relatively small. Inferred.

Next, in step S2, the sensor output V from the sensor element 10 is taken in, and it is determined whether or not the output value V0 which is a threshold value has been reached. If the sensor output V is less than the output value V0, a negative determination is made in step S2, and the process returns to step S1 to continue electrostatic collection and sensor output V capture.

In step S2, when the sensor output V reaches the output value V0, it is determined that the timing for calculating the number of particles of the particulate matter has been reached, and the process proceeds to step S3. . At this time, the particulate matter is deposited and electrically connected between the pair of electrodes 21 and 22. Steps S3 to S7 are processing as the particle number calculation unit 42 of the ECU 4. Of these, step S3 is processing as the voltage control unit 421, and step S4 is processing as the interelectrode resistance detection unit 422.

In step S3, the voltage applied between the pair of electrodes 21 and 22 of the sensor element 10 is changed from the first voltage to a lower second voltage. At this time, the state in which the deposited particulate matter is electrically connected changes. Further, in step S4, the interelectrode resistance R between the pair of electrodes 21 and 22 at the second voltage as the detection voltage is measured. Then, it progresses to step S5 and estimates the average particle diameter D of a particulate matter based on the measured resistance R between electrodes.

As described above, the second voltage applied in step S3 may be a voltage different from the first voltage, for example, a voltage lower than the first voltage. Preferably, the difference between the first voltage and the second voltage is preferably large. For example, the difference is set in advance using the relationship between the applied voltage and the interelectrode resistance R shown in FIG. This relationship is measured using the model exhaust gas purification apparatus shown in FIG. 10, and the PM generator 100 that generates particulate matter mainly made of soot in the model exhaust gas flow path 101 in which the DPF 5 is installed. Is connected. The particulate matter detection sensor 1 is arranged on the upstream side of the DPF 5, and a commercially available particle size distribution measuring device (that is, EPSS: Engine Exhaust Particle Sizer) 102 is arranged on the upstream side of the particulate matter detection sensor 1. Is done.

Using this model exhaust gas purification device, PM collection by the particulate matter detection sensor 1 was performed by changing the average particle diameter D of the particulate matter contained in the model exhaust gas. When the sensor output V reaches a predetermined output value V0 (for example, 0.12 V) set in advance, PM collection is stopped and the PM generator 100 is stopped. In this state, the applied voltage to the particulate matter detection sensor 1 was changed, and the interelectrode resistance R between the pair of electrodes 21 and 22 was measured. Measurement conditions were as follows.
Model gas temperature: 200 ° C
Model gas flow rate: 15m / s
Average particle diameter D: 74 nm, 63 nm, 58 nm
Applied voltage when collecting PM: 35V
Applied voltage at the time of measurement: 1V (not measurable), 5V, 10V, 20V, 30V, 35V
Electrode spacing: 20 μm

As shown in FIG. 9, the average particle diameter D decreases as the applied voltage (that is, detection voltage = second voltage) at the time of measurement becomes lower than the applied voltage (that is, the first voltage) during PM collection. The difference in inter-electrode resistance R due to increases. For example, when the applied voltage at the time of PM collection and measurement remains the same (that is, 35 V) without changing to the second voltage, there is no sufficiently large difference. Compared with this, as the applied voltage at the time of measurement becomes lower than 35 V, the interelectrode resistance R increases, and the difference in the interelectrode resistance R due to the average particle diameter D increases. Thus, it becomes possible to estimate the average particle diameter D from the interelectrode resistance R by changing to a lower second voltage.

Specifically, as shown in FIG. 11, the average particle diameter D (unit: nm) of the particulate matter and the interelectrode resistance R (unit: Ω) are in a proportional relationship, and a straight line representing these relationships The slope (unit: Ω / nm) increases as the applied voltage decreases, as shown in FIG. In particular, in the region where the applied voltage at the time of measurement is about 20 V or lower, the slope increases rapidly. Therefore, more preferably, the second voltage is set to about 60% of the first voltage (for example, when the first voltage is 35V, the second voltage is 20V) or less. Thereby, the estimation precision of the average particle diameter D based on resistance R between electrodes can be improved more.

In the region where the applied voltage at the time of measurement was very low (for example, detection voltage = 1V), the measurement variation was large, so it was not shown in FIG. Therefore, when the second voltage as the detection voltage is selected, for example, the current flowing between the pair of electrodes 21 and 22 at the time of resistance measurement is 1 μA so that the measurement can be performed in accordance with the circuit configuration. It is desirable to set a voltage that is about a lower limit value so as not to be lower than that. Thereby, the measurement accuracy of the interelectrode resistance R in step S4 can be improved, and the circuit cost can be reduced.

In step S5, based on the measured interelectrode resistance R, for example, the average particle diameter D of the particulate matter is estimated using the relationship shown in FIG. In FIG. 13, the horizontal axis represents the reciprocal of the average particle diameter D (that is, the median diameter), and the interelectrode resistance R on the vertical axis increases as the average particle diameter D increases. Further, the interelectrode resistance R increases as the second voltage, which is the applied voltage at the time of measurement, decreases.
As shown in FIG. 14, this is different in the case where the average particle diameter D is small and large, when the arrangement of the particulate matter collected by the applied voltage level is changed. This is probably because of this. That is, in the state collected at the first voltage, the applied voltage is relatively high and the electric field strength between the pair of electrodes 21 and 22 is high. In that case, the state in which the particulate matter (that is, PM in the figure) arranged between both electrodes is aligned and electrically connected to each other is largely different depending on the average particle diameter D. Does not occur. Further, when the second voltage is a relatively high voltage, the change in the electric field strength is small and the change in the collection state is also small. That is, the arrangement of the particulate matter is substantially the same as the state in which the sensor output V at the time of PM collection reaches the predetermined output value V0. For this reason, there is no significant difference in the measured interelectrode resistance R.

On the other hand, when the applied voltage is further lowered, the electric field strength between the pair of electrodes 21 and 22 is further reduced, so that the force for restraining the particulate matter is weakened. Then, as shown in the drawing, it is considered that the alignment state of the particulate substances is disturbed, and the contact resistance between the adjacent particulate substances is increased. Further, the contact state of the particulate matter connecting the pair of electrodes 21 and 22 (for example, the formation state of the conductive path) is changed, and the change is larger than that in the case where the average particle size D is relatively small. Tends to be prominent when is relatively large.
Here, since the particulate matter has a higher resistance as the particle diameter is smaller, when the predetermined sensor output V0 is reached, more particulate matter is collected as the particle diameter of the particulate matter is smaller. Since the interelectrode resistance R becomes the combined resistance of the contact resistance of the particulate matter and the resistance depending on the contact state, the change in the interelectrode resistance R is smaller as the particle size is smaller. Become.

As described above, since the change in the interelectrode resistance R changes depending on the particle size of the collected particulate matter, the second state is changed to a second voltage different from that at the time of collecting the particulate matter, and the collection state is changed. Thereafter, the average particle diameter D of the particulate matter can be estimated by measuring the interelectrode resistance R.
Therefore, these relationships are examined in advance for each operation condition and measurement condition, stored in a ROM as a storage area of the ECU 4 as a relational expression or a map, and the average particle diameter D is estimated from the measured interelectrode resistance R. be able to. The average particle diameter D obtained by this process is the average particle diameter of the particulate matter discharged downstream of the DPF 5 during the collection period from the start of electrostatic collection in step S1 to the arrival of the determination timing in step S2. is there.

Next, the process proceeds to step S6, where the mass M of the particulate matter discharged during the collection period is estimated from the sensor output V. The sensor output V has a substantially positive correlation with the mass M of the particulate matter collected by the detection unit 2 of the sensor element 10 during the collection period. Here, when the determination in step S2 is affirmative Sensor output V, ie, a predetermined output value V0 is used. In step S2, it is determined whether or not the sensor output V has reached the output value V0, and the sensor output V at the time when the determination is affirmative is substantially equal to the output value V0 that is a threshold value.

Furthermore, it progresses to step S7 and calculates the particle number N of a particulate matter by the following formula 2 and formula 3 using the mass M of the estimated particulate matter, and the average particle diameter D.
Equation 2: number of particles N = mass M / PM average volume × PM gravity formula 3: PM Average volume ^{= 4π (D / 2) 3} /3
Here, the specific gravity (that is, PM specific gravity) of the particulate matter can be a predetermined constant value (for example, 1 g / cm ³ ). The average volume of the particulate matter (that is, the PM average volume) is calculated from the estimated average particle diameter D of the particulate matter, by regarding the particulate matter as a sphere, by the above Equation 3.

When the particle number N of the particulate matter calculated through the series of steps is compared with the actually measured particle number, as shown in FIG. 15, the relationship between the estimated PM number and the actually measured PM number almost coincides. It was confirmed that Thus, by considering the average particle diameter D of the particulate matter, the number N of particles of the particulate matter can be accurately estimated.

(Embodiment 2)
In the particulate matter detection device of the second embodiment, the basic configuration of the particulate matter detection sensor 1 as a sensor unit and the ECU 4 as a sensor control unit is the same as that of the first embodiment. In the first embodiment, the average particle diameter D of the particulate matter is estimated based on the interelectrode resistance R in the second voltage as the detection voltage, but a plurality of voltages lower than the first voltage are set as the detection voltage. However, the interelectrode resistance R may be measured at a plurality of voltages having different magnitudes. The plurality of voltages may include a voltage having the same magnitude as the second voltage. Details of the particulate matter detection process executed by the ECU 4 in this case will be described with reference to FIG.
Of the reference numerals used in the second and subsequent embodiments, the same reference numerals as those used in the above-described embodiments represent the same components as those in the above-described embodiments unless otherwise indicated.

As shown in the flowchart in FIG. 16, in this embodiment, the particulate matter detection process executed by the ECU 4 that is the sensor control unit is obtained by changing a part of the procedure of the first embodiment shown in FIG. 7. Specifically, since steps S11 to S14 are the same as steps S1 to S4 in FIG. 7, the description will be simplified, and steps S15 and after that will be different will be mainly described.

In steps S11 to S14, electrostatic collection is performed by applying a first voltage to the pair of electrodes 21 and 22 of the detection unit 2, and when the sensor output V reaches the output value V0, it is changed to the second voltage and captured. After changing the collection state, the interelectrode resistance R is measured at the second voltage. Next, proceeding to step S15, the voltage applied to the pair of electrodes 21 and 22 is changed to a third voltage lower than the second voltage, and further proceeding to step S16 to measure the interelectrode resistance R1 at the third voltage. To do.

Here, the second voltage and the third voltage as the detection voltages may be voltages that are lower than the first voltage and different in magnitude from each other. Preferably, at least one or both of the second voltage and the third voltage is about 60% or less of the first voltage, and the lower the applied voltage, the more accurate the average particle diameter D is estimated. Get higher. Further, it is more preferable that the difference between the second voltage and the third voltage is relatively large.

In step S17, the average particle diameter D is estimated based on the resistance values at a plurality of voltages serving as detection voltages, that is, the interelectrode resistance R at the second voltage and the interelectrode resistance R1 at the third voltage. For example, similarly to step S5 of FIG. 7 described above, the average particle diameter D can be estimated for each of the interelectrode resistances R and R1 using the relationship shown in FIG. 13, and the average value thereof can be calculated. . Preferably, when estimating the average particle diameter D, the estimation accuracy can be increased by weighting each voltage. Specifically, it is preferable to weight the interelectrode resistances R and R1 so that the weight is increased as the measured voltage is lower.

The subsequent steps S18 and S19 are the same as steps S6 and S7 in FIG. That is, in step S18, the mass M of the particulate matter is estimated using the output value V0 as the sensor output V when step 12 is positively determined. Further, in step S19, the number N of the particulate matter is calculated by the above formulas 2 and 3 using the estimated mass M of the particulate matter and the average particle diameter D.

Thus, by measuring the interelectrode resistances R and R1 at a plurality of voltages, the average particle diameter D can be estimated more accurately. The plurality of voltages are not limited to two different voltages as in the present embodiment, but three or more different voltages can be set and the interelectrode resistance R can be measured for each of them. As shown in an example in FIG. 17, under an applied voltage condition (that is, the particulate matter detection process according to the first embodiment) where the applied voltage at which the interelectrode resistance R is measured is one, the estimated particle diameter and the actually measured particle diameter are The maximum difference between the two is about 16%. On the other hand, as shown in FIG. 18, when the interelectrode resistance R is measured under a plurality of applied voltage conditions, the difference between the estimated particle diameter and the actually measured particle diameter is about 5% at the maximum. Can be reduced.

(Embodiment 3)
In the particulate matter detection device of the third embodiment, the basic configuration of the particulate matter detection sensor 1 as a sensor unit and the ECU 4 as a sensor control unit is the same as that of the second embodiment. Also in this embodiment, a plurality of voltages lower than the first voltage are set as detection voltages, and the interelectrode resistance R is measured at each of the plurality of voltages. At this time, in Embodiment 2 above, the average particle diameter D was estimated from the measured interelectrode resistance R, but based on the slope I in the relationship between the plurality of voltages and the measured interelectrode resistance R, the average particle diameter D may be estimated.
In that case, the particle number calculation unit 42 of the ECU 4 shown in FIG. 1 calculates the slope in the relationship between the plurality of voltages and the interelectrode resistance R in addition to the voltage control unit 421 and the interelectrode resistance detection unit 422. An unillustrated inclination calculation unit is provided. Details of the particulate matter detection process executed by the ECU 4 in this case will be described with reference to FIG.

As shown in the flowchart in FIG. 19, in this embodiment, the particulate matter detection process executed by the ECU 4 that is the sensor control unit is obtained by changing a part of the procedure of the second embodiment shown in FIG. 16. Specifically, the only difference is that step S17 for estimating the average particle diameter D is performed in two stages of steps S171 and S172. Step S171 is processing as an inclination calculation unit, and steps S11 to S16 and S18 to S19 are the same processing as in FIG.

Here, as shown in comparison with FIGS. 20 and 21, the measured interelectrode resistance R may fluctuate due to the influence of disturbances such as the measured temperature. FIG. 21 shows a case where the measured temperatures are all set correctly. Even when the average particle diameter D of the particulate matter is in a relatively close range (for example, 65.2 nm, 54.7 nm, 52. 3 nm, 48.5 nm), the relationship between the applied voltage and the interelectrode resistance R shows a good correlation with the average particle size D. In the drawing, the variation range of the inter-electrode resistance R at each applied voltage is shown. For example, even in the case of 54.7 nm and 52.3 nm where the difference in the average particle diameter D is small, there is almost no variation range overlap. The average particle diameter D can be estimated by the procedure of the second embodiment.

However, these relationships are temperature-dependent. For example, the interelectrode resistance R deviates from the original value due to the influence of disturbance such as the temperature of the sensor element 10 at the time of measurement deviating from the set temperature. Sometimes. FIG. 20 shows the result of measuring the interelectrode resistance R at a measurement temperature lower by 50 ° C. only when the average particle diameter D is 52.3 nm. Compared to FIG. 21, the average particle diameter D is 54.7 nm. It approaches the value of the interelectrode resistance R. Therefore, as shown in FIG. 22 where the applied voltage is 5 V, the reciprocal of the average particle diameter D and the interelectrode resistance R show a good correlation as a whole, but under conditions where the temperature is low (that is, in FIG. 22). Since the value of the interelectrode resistance R is large when there is no disturbance, the estimation accuracy may be reduced.

Even in such a case, the slope I of the approximate expression (that is, the approximate straight line expression shown in FIG. 20) that linearly approximates the relationship between the applied voltage and the interelectrode resistance R is a constant value. This is because the same displacement occurs in the interelectrode resistance R at each applied voltage due to the influence of the disturbance. As shown in FIG. Is not affected by disturbance (ie, indicated by white circles in FIG. 23). Therefore, the estimation accuracy can be improved by estimating the average particle diameter D using the slope I.

In the flowchart shown in FIG. 19, according to steps S11 to S16, electrostatic collection is performed at the first voltage, and after the sensor output V reaches the output value V0, the second voltage is changed. The interelectrode resistances R and R1 at the third voltage are measured. Next, the process proceeds to step S171, and an inclination I of an approximate expression that linearly approximates these relationships is calculated from the second voltage, the third voltage, and the interelectrode resistances R and R1. In step S172, the average particle diameter D of the particulate matter can be accurately estimated from the calculated slope I of the approximate expression based on the relationship shown in FIG.

Thereafter, the process proceeds to steps S18 to S19, where the mass M of the particulate matter is estimated based on the output value V0, and the number N of particulate matter particles is calculated using this mass M and the average particle size D. Can do.

(Embodiment 4)
In the particulate matter detection device of the fourth embodiment, the basic configuration of the particulate matter detection sensor 1 as a sensor unit and the ECU 4 as a sensor control unit is the same as that of the first embodiment. In the first and second embodiments, the heater unit 3 of the particulate matter detection sensor 1 is used for the regeneration of the detection unit 2 prior to the collection of the particulate matter. However, when detecting the number N of particles, the detection unit 2 is used. It can also be used for heat treatment of particulate matter deposited on the substrate. At that time, the heating control unit 43 of the ECU 4 energizes the heater unit 3 so that the temperature of the detection unit 2 is lower than that at the time of regeneration, for example, SOF in the accumulated particulate matter can be volatilized and the soot does not burn. Heat to a suitable temperature. In this case, the details of the particulate matter detection process executed by the ECU 4 will be described with reference to FIG.

As shown in the flowchart in FIG. 24, in this embodiment, the particulate matter detection process executed by the ECU 4 serving as the sensor control unit is obtained by changing a part of the procedure of the first embodiment shown in FIG. Specifically, steps S21 to S22 are the same processing as steps S1 to S2 in FIG. In step S23, electric power is supplied to the heater unit 3 of the sensor element 10 to heat the detection unit 2, and the temperature is raised to a first temperature at which only SOF is volatilized and removed, and soot is not removed.

25. As shown in FIG. 25 as an example of the heat treatment pattern, the first temperature, which is the heat treatment temperature, is selected in the range of 200 ° C. or higher and 400 ° C. or lower (for example, 350 ° C.). At this time, the heating control unit 43 starts heating after the time point when the output value V0 is reached, and controls the temperature increase rate so as to converge to a predetermined first temperature. For example, the temperature rising rate can be kept constant until the vicinity of the first temperature, and then the temperature rising rate can be gradually reduced to converge to the first temperature.

At this time, as the temperature of the detection unit 2 rises due to the operation of the heater unit 3 and converges to the first temperature, the sensor output V also draws a similar curve and converges to the first output value V1 at the first temperature. To do. At that time, the detection unit 2 is heated and SOF is volatilized, and only the soot is used to improve the conductivity. Therefore, the first output value V1 is generally larger than the output value V0. This also includes a temperature-specific effect that lowers the resistance of the soot due to a temperature rise.

Therefore, in step S24, after reaching the first temperature, the first output value V1 at the first temperature is captured. The time required to reach the first temperature is the time necessary to heat and hold until the first temperature is reached and the SOF is sufficiently volatilized, and can be arbitrarily set by conducting a test or the like in advance.

Subsequent steps S25 to S27 are the same processes as steps S3 to S5 in FIG. In step S25, the voltage applied to the pair of electrodes 21 and 22 of the detection unit 2 is changed from the first voltage to the second voltage, and the process further proceeds to step S26, where the interelectrode resistance in the second voltage as the detection voltage is reached. Measure R. Then, it progresses to step S27 and estimates the average particle diameter D of a particulate matter based on the measured resistance R between electrodes.

As described above, when detecting particulate matter, the influence of SOF in the discharged particulate matter is not necessarily great. However, for example, since the SOF is less likely to volatilize under conditions where the exhaust temperature is low, the SOF ratio in the particulate matter tends to increase. As shown in FIG. 26, the relationship between the resistance R between electrodes measured before and after the heat treatment and the average particle diameter D shows a large difference in resistance value depending on the presence or absence of the heat treatment. It can be seen that the detection error is reduced by volatilizing.

Next, the process proceeds to step S28, and the mass M of the particulate matter collected by the detection unit 2 of the sensor element 10 during the collection period is estimated based on the first output value V1. The first output value V1 is a sensor output V based on the particulate matter mainly composed of Soot, and has a positive correlation with the mass M of the particulate matter. By examining this relationship in advance and storing it in the ROM, which is the storage area of the ECU 4, the mass M can be estimated.

Thereafter, the process proceeds to step S29, and the number N of particles of the particulate matter is calculated from the estimated mass M of the particulate matter and the average particle diameter D in the same procedure as in step S7 of FIG. Thus, the influence of SOF and exhaust temperature can be eliminated by performing the heat treatment of the detection unit 2 after collection.

(Embodiment 5)
In the particulate matter detection device of the fifth embodiment, the basic configuration of the particulate matter detection sensor 1 as a sensor unit and the ECU 4 as a sensor control unit is the same as that of the first embodiment. In addition, the procedure for eliminating the influence of SOF by performing the heat treatment of the detection unit 2 after collection by the heating control unit 43 of the ECU 4 is the same as in the fourth embodiment, and the mass M of the particulate matter is estimated. Only the procedure is different.

Specifically, in the flowchart shown in FIG. 27, among the particulate matter detection processing executed by the ECU 4, steps S31 to S37 are the same as steps S21 to S27 of the fourth embodiment shown in FIG. The average particle diameter D of the particulate matter is accurately estimated by changing to the second voltage after the heat treatment and measuring the interelectrode resistance R.

Thereafter, the process proceeds to step S38, and the mass M of the particulate matter collected by the detection unit 2 of the sensor element 10 during the collection period is estimated based on the output value V0 that is the sensor output V in step 32. Since the SOF ratio in the mass M of the particulate matter is relatively small, the mass M of the particulate matter can be estimated based on the output value V0 as in the first embodiment. Thereafter, in step S39, the number N of particulate matter particles can be calculated using the estimated mass M of the particulate matter and the average particle diameter D.

(Embodiment 6)
In the particulate matter detection process in each of the embodiments described above, the case where the particulate matter detection sensor 1 is the laminated sensor element 10 having the detection unit 2 having the laminated structure is mainly described. As described above, the print type sensor element 10 in which the pair of electrodes 21 and 22 are formed by printing on the surface of the rectangular parallelepiped insulating base 11 can be provided. In this case, the distance between the pair of electrodes 21, 22, that is, the electrode interval is wider than that of the laminated sensor element 10, and can be appropriately selected within a range of 50 μm to 500 μm, for example.

Further, in the case of the print type sensor element 10, as shown in FIGS. 28 to 29, the detection conductive portion 23 can be disposed on the surface of the insulating base 11 serving as the base. The detection conductive portion 23 is a conductive material having a higher electrical resistivity than the particulate matter, and is made of a high-resistance conductive material described later.
The particulate matter detection process executed by the ECU 4 is formed not only with a configuration in which the pair of electrodes 21 and 22 of the sensor element 10 is formed of an insulating material as in the above embodiments, but also with a high-resistance conductive material. This is also effective for the configuration described above, and will be described below.

The conductive portion for detection 23 is arranged on the surface of the distal end side in the longitudinal direction X (that is, one end side in FIG. 28) to be the detection portion 2. The pair of electrodes 21, 22 are arranged so as to extend in the longitudinal direction X with a spacing from the surface of the detection conductive portion 23 (that is, the surface opposite to the base 11). The pair of electrodes 21 and 22 are connected to linear lead electrodes 21a and 22a extending from the distal end side of the insulating base 11 to the proximal end side (that is, the other end side in FIG. 28), respectively. The pair of electrodes 21 and 22 may have a configuration in which a plurality of pairs of electrodes are arranged in, for example, a comb-like shape, similarly to the sensor element 10 shown in FIG.

Here, as shown in FIG. 30, the high resistance conductive material 20 used for the detection conductive portion 23 has a surface electrical resistivity of 1.0 × 10 ⁷ to 1.0 in a temperature range of 100 to 500 ° C. A conductive material in the range of × 10 ¹⁰ Ω · cm is desirable. As a conductive material whose surface electrical resistivity satisfies the above numerical range, for example, ceramics having a perovskite structure whose molecular formula is represented by ABO ₃ can be used. In the molecular formula, the A site is at least one selected from La, Sr, Ca, and Mg, and the B site is at least one selected from Ti, Al, Zr, and Y. Preferably, perovskite-type ceramics (ie, Sr _1-X La _X TiO ₃ ), in which the main component is Sr and the subcomponent is La and the B site is Ti, is used for the A site.

In FIG. 30, when x in (Sr _1-X La _X TiO ₃ ) is in the range of 0.016 to 0.036 so as to show the relationship between the surface resistivity ρ of the perovskite ceramic and the temperature. The surface electrical resistivity ρ is 1.0 × 10 ⁷ to 1.0 × 10 ¹⁰ Ω · cm in the temperature range of 100 to 500 ° C. Therefore, such ceramics (for example, Sr _0.984 La _0.016 TiO ₃ , Sr _0.98 La _0.02 TiO ₃ , Sr _0.964 La _0.036 TiO ₃ ) are preferably used as a material for constituting the detection conductive portion 23. it can.

Here, the “surface electrical resistivity ρ” is calculated by creating the sample S shown in FIG. 31, measuring the electrical resistance between the measurement electrodes 101 and 102 (that is, the interelectrode resistance), and using the following formula 4. Means the value.
In this embodiment, the surface electrical resistivity ρ of the conductive material is measured as follows. That is, first, a sample S shown in FIG. 31 is created. This sample S is made of a conductive material and has a plate-like substrate 100 having a thickness T of 1.4 mm, and a pair of measuring electrodes 101 formed on the main surface of the plate-like substrate 100 and having a length L and a distance D. , 102. Such a sample S is formed, and the electrical resistance R (unit: Ω) between the pair of measurement electrodes 101 and 102 is measured. The surface electrical resistivity ρ is calculated by the following equation 4.
Formula 4: ρ = R × L × T / D

In this specification, the simple description of “electrical resistivity” means so-called bulk electrical resistivity. For example, as shown in FIG. 32, a bulk sample S1 including a substrate portion 200 made of a conductive material and a pair of measurement electrodes 201 and 202 formed on the side surface of the substrate portion 200 is prepared. It can be calculated by measuring the electrical resistance between the measurement electrodes 201 and 202.

As shown in FIG. 30, when La is not added (SrTiO ₃ ), the surface electrical resistivity ρ is about 1.0 × 10 ⁵ to 1.0 × 10 ¹¹ Ω in the temperature range of 100 to 500 ° C. It is cm, and is out of the range of 1.0 × 10 ⁷ to 1.0 × 10 ¹⁰ Ω · cm on the low temperature side and the high temperature side. From this result, it can be seen that when La is added to the ceramic, the change in surface electrical resistivity ρ due to temperature is small.

In addition, in acquiring the graph of FIG. 30, the measurement of surface electrical resistivity (rho) was performed as follows in detail. That is, ceramics with x in Sr _1-X La _X TiO _{3 set to} 0, 0.016, 0.02, 0.36 are prepared, and a sample S (for example, see FIG. 31) is prepared using these ceramics. did. Each sample S has a plate-like substrate 100 having a thickness T of 1.4 mm and a pair of measuring electrodes 101 and 102 formed on the main surface of the plate-like substrate 100 and having a length L of 16 mm and a distance D of 800 μm. With. Then, the sample S was heated to 100 to 500 ° C. in the atmosphere, a voltage of 5 to 1000 V was applied between the measuring electrodes 101 and 102, and the electric resistance R was measured. And the surface electrical resistivity (rho) was computed using the said Formula 4.

In the present embodiment, any of the first to fifth embodiments may be applied to the particulate matter detection process executed by the ECU 4 serving as the sensor control unit. That is, when the particulate matter is collected, the first voltage is applied to quickly reach the threshold, and then, for example, the second voltage lower than the first voltage is changed, and then detected at the second voltage or a plurality of voltages. The average particle diameter D can be accurately estimated from the resistance value. Furthermore, the number N of particles in the collection period is calculated from the mass M of the particulate matter estimated using the output value V0 or the first output value V1 after the heat treatment and the PM specific gravity which is a known constant. Can do.

Specifically, the same processing as steps S1 to S7 of the first embodiment shown in FIG. 7 can be performed.
That is, in steps S1 to S3, the first voltage is applied to the pair of electrodes 21 and 22 of the detection unit 2 to perform electrostatic collection, and when the sensor output V reaches the output value V0, the second voltage is changed. Then, in step S4, the interelectrode resistance R at the second voltage as the detection voltage is measured, and in step S5, the average particle diameter D of the particulate matter is calculated from the interelectrode resistance R in step S4. presume. In steps S6 to S7, the mass M of the particulate matter is estimated based on the output value V0, and the number N of particulate matter particles is determined using the specific gravity of the particulate matter and the estimated mass M of the particulate matter. Is calculated.

As shown in FIG. 33, also in the detection unit 2 using the detection conductive unit 23, the relationship between the applied voltage and the interelectrode resistance is such that the average particle diameter D (for example, 56.9 nm, 65. 4 nm, 80.0 nm) shows a tendency that the difference in inter-electrode resistance R increases.
Measurement conditions were as follows.
Model gas temperature: 200 ° C
Model gas flow rate: 15m / s
PM concentration: 10 mg / m ³
Surface electrical resistivity ρ: 2.4 × 10 ⁸ Ω · cm
Average particle diameter D: 56.9 nm, 65.4 nm, 80.0 nm
Electrode spacing: 60 μm x 5 sets Number of particles N: 1 to 2 x 10 ¹⁴

Therefore, when the voltage is changed to a lower second voltage (for example, 5 V) with respect to the applied voltage at the time of PM collection (that is, the first voltage: for example, 35 V), the interelectrode resistance R increases as the average particle diameter D increases. Becomes larger. As shown in FIG. 34, in the relationship between the reciprocal of the average particle diameter D and the interelectrode resistance R, the interelectrode resistance R increases as the reciprocal of the average particle diameter D decreases. Using this relationship, the average particle diameter D of the particulate matter can be estimated with high accuracy.

As shown in FIG. 35, the detection unit 2 of the present embodiment has a pair of electrodes 21 and 22 arranged on the surface of the high-resistance conductive material 20 that becomes the detection conductive unit 23. Even in the initial state in which no PM is deposited, a minute current (for example, indicated by an arrow in the drawing) flows between the electrodes 21 and 22 via the high-resistance conductive material 20. In this state, as shown in FIG. 36, when particulate matter adheres to the surface of the high-resistance conductive material 20, the inter-electrode resistance R between the pair of electrodes 21 and 22 becomes high-resistance conductive material 20 and particulate matter. This is the combined resistance. Therefore, the inter-electrode resistance R changes as much as the particulate matter adheres, and the high resistance conductive material 20 has a higher electrical resistivity than the particulate matter. Therefore, as shown in FIG. Sensor output increases in proportion to.

FIG. 38 shows a comparison of the number of particles N of the particulate matter calculated through these series of steps with the number of particles actually measured, and the estimated number of PMs and the number of measured PMs have a correlation. confirmed. When the electrodes are formed of an insulator as in each of the above embodiments, the sensor output cannot be obtained until the particulate matter is short-circuited between the electrodes as in FIG. 4 described above. Particulate matter can be detected with a smaller amount of deposition than short-circuiting. Therefore, the number N of particles can be calculated even with a small amount of particulate matter.

(Embodiment 7)
In the particulate matter detection device of the seventh embodiment, the basic configuration of the particulate matter detection sensor 1 as a sensor unit and the ECU 4 as a sensor control unit is the same as that of the first embodiment. In each of the above embodiments, the mass M of the particulate matter is calculated with the specific gravity of the particulate matter as a constant value, but instead of using the PM specific gravity as a known constant, based on the estimated average particle diameter D You may make it estimate PM specific gravity. In this case, the details of the particulate matter detection process executed by the ECU 4 will be described with reference to FIG.

As shown in the flowchart in FIG. 39, in this embodiment, the particulate matter detection process executed by the ECU 4 serving as the sensor control unit is performed in steps S41 to S45 from steps S1 to S5 in the first embodiment shown in FIG. Is the same process. That is, electrostatic collection is performed by applying a first voltage to the pair of electrodes 21 and 22 of the detection unit 2, and when the sensor output V reaches the output value V0, the collection state is changed by changing to the second voltage. Let Thereafter, the process proceeds to step S44, in which the interelectrode resistance R at the second voltage as the detection voltage is measured. In step S45, the average particle diameter D of the particulate matter is estimated from the interelectrode resistance R.

Thereafter, in step S46, the specific gravity of the collected particulate matter is estimated from the estimated average particle diameter D. As shown in FIG. 40, there is a correlation between the average particle diameter D (unit: nm) and the specific gravity (unit: g / cm ³ ), and it has been found that the PM specific gravity decreases as the average particle diameter D increases. . Therefore, based on this relationship, the specific gravity at the estimated average particle diameter can be accurately calculated from the relational expression of the average particle diameter D and PM specific gravity prepared in advance.

Next, in step S47, the mass M of the particulate matter is estimated based on the output value V0. Further, in step S48, the particulate matter is estimated using the estimated specific gravity of the particulate matter and the mass M of the particulate matter. The number N of particles of the substance can be calculated.
Note that the method of estimating the average particle diameter D of the particulate matter that is the basis for calculating the specific gravity is not limited to the method of estimating from the interelectrode resistance R shown here, but the method of estimating from the amplification factor of the sensor output due to heating, high frequency It is also possible to use a method of estimating from the impedance.

FIG. 41 shows the relationship between the number N of particulate matter calculated using a known PM specific gravity and the number of measured particles without performing the estimation of the PM specific gravity in step S46 in the series of steps. The estimated number of PMs is in a range of about ± 20% of the actually measured PM number. On the other hand, as shown in FIG. 42, when the PM specific gravity estimated in step S46 is used, the difference between the estimated PM number and the actually measured PM number is smaller, and the detection accuracy of the particle number N is improved. Can be improved.

(Embodiment 8)
In the particulate matter detection device of the eighth embodiment, the basic configuration of the particulate matter detection sensor 1 as a sensor unit and the ECU 4 as a sensor control unit is the same as that of the sixth embodiment. The sensor element 10 includes a detection unit 2 using a detection conductive unit 23 capable of detecting a minute amount of particulate matter. In the sixth embodiment, as in the first embodiment, after changing from the first voltage to the second voltage, the interelectrode resistance R was measured with the second voltage as the detection voltage. The voltage is changed to a detection voltage (for example, a third voltage) different from the two voltages, and the interelectrode resistance R is measured. Details of the particulate matter detection process executed by the ECU 4 in this case will be described with reference to FIG.

As shown in the flowchart in FIG. 43, in this embodiment, the particulate matter detection process executed by the ECU 4 that is the sensor control unit is obtained by changing a part of the procedure of the first embodiment shown in FIG. Specifically, steps S51 to S53 are the same as steps S1 to S3 in FIG. 7, and electrostatic collection is performed by applying a first voltage to the pair of electrodes 21 and 22 of the detection unit 2, When the sensor output V reaches the output value V0, the collection state is changed by changing to the second voltage. Subsequently, it progresses to step S54 and changes the applied voltage to a pair of electrodes 21 and 22 of the detection part 2 from a 2nd voltage to a 3rd voltage.

Here, as described above, as the second voltage is lower than the first voltage (for example, 35 V) at the time of PM collection, the collection state of the particulate matter changes and the change in the interelectrode resistance R changes. growing. However, since the sensor output decreases as the detection voltage decreases, in this case, it is preferable to measure the interelectrode resistance R by changing the change in the interelectrode resistance R to a third voltage that can be easily discriminated. As shown in FIG. 44, when a third voltage (for example, 20 V) higher than the second voltage (for example, 0 V) is set, the average particle diameter D and the interelectrode resistance R show a clear proportional relationship. . Measurement conditions were as follows.
Model gas temperature: 200 ° C
Model gas flow rate: 15m / s
PM concentration: 1 mg / m ³
Surface electrical resistivity ρ: 3.8 × 10 ⁸ Ω · cm
Electrode interval: 60 μm x 9 sets

Therefore, from the relationship shown in FIG. 44, the second voltage and the third voltage in steps S53 and S54 are set to, for example, 0 V and 20 V, and the process proceeds to step S55, where the interelectrodes at the third voltage as the detection voltage are set. Measure resistance R. Further, the process proceeds to step S56, and the average particle diameter D of the particulate matter can be accurately estimated based on the measured interelectrode resistance R and the relationship shown in FIG. Then, after estimating the mass M of the particulate matter from the output value V0 in step S57, the number N of particulate matter particles is calculated in step S58.
FIG. 45 shows the relationship between the number of particles N of the particulate matter calculated by the series of steps and the number of actually measured particles, and there is a good correlation between the estimated number of PMs and the number of actually measured PMs.

46 to 49 show modifications of this embodiment. When detecting a very small amount of particulate matter, for example, a third voltage, which is a detection voltage, is applied during PM collection according to the sensor output characteristics. It is good also as a voltage higher than the 1st voltage (for example, 35V). The measurement conditions in this example were as follows.
Model gas temperature: 200 ° C
Model gas flow rate: 15m / s
PM concentration: 1 mg / m ³
Surface electrical resistivity ρ: 1.0 × 10 ¹⁰ Ω · cm
Average particle diameter D: 55 nm, 61 nm, 66 nm
Electrode spacing: 80 μm × 9 sets Number of particles N: about 1 × 10 ¹³

As shown in FIG. 46, even when the number N of particles is very small, the tendency that the interelectrode resistance R increases as the applied voltage decreases is the same, but the difference in the interelectrode resistance R due to the average particle size D is large. Becomes smaller. Therefore, as shown in FIG. 47, when the sensor output at the time of PM collection (that is, the measurement current) is reduced and the detection voltage is lowered, the measured current is further reduced and becomes the measurement limit, and the average particle diameter The difference of D cannot be seen.

In that case, after changing to the second voltage (for example, 0V), as shown in FIG. 48, on the side higher than the first voltage (for example, 35V), the measured current (that is, the electrode) by the average particle diameter D is set. An arbitrary voltage with which the difference in the resistance change amount) can be determined can be set as the third voltage. For example, as shown in FIG. 49, when the third voltage is 60 V, the difference in the amount of change in the interelectrode resistance R with respect to the average particle diameter D is sufficiently large. Therefore, the average particle diameter D can be estimated using this relationship, and the number N of particles can be calculated.

FIG. 50 shows a modification of the present embodiment, in which the second voltage (for example, 70 V) and the third voltage (for example, 70 V) are set to higher voltages with respect to the first voltage (for example, 35 V). The relationship between the average particle diameter D and the amount of change in the interelectrode resistance R is shown.
Similar to the detection voltage, the second voltage can be higher than the first voltage, and the change in the collection state can be increased by increasing the difference. In this case, the second voltage and the detection voltage can be set to the same voltage, and the interelectrode resistance R can be measured without changing the applied voltage.

As shown in FIG. 50, even when the number N of particles is very small, by setting the second voltage and the third voltage sufficiently higher than the first voltage, the amount of change in the interelectrode resistance R due to the average particle diameter D can be reduced. The difference can be sufficiently discriminated. Therefore, using this relationship, the average particle diameter D can be estimated and the number N of particles can be calculated.

FIG. 51 is a modification of the present embodiment, and after changing from a first voltage (for example, 35V) to a lower second voltage (for example, 0V), a higher detection voltage (that is, a third voltage; , 35 V), the relationship between the average particle diameter D and the interelectrode resistance R is shown. The measurement conditions in this example are as follows, and the particulate matter detection sensor 1 uses a sensor element 10 including a print-type detection unit 2 that does not use the detection conductive unit 23.
Model gas temperature: 200 ° C
Model gas flow rate: 15m / s
PM concentration: 10 mg / m ³

As shown in FIG. 51, even when the detection voltage is the same voltage as the first voltage, the interelectrode resistance R due to the average particle diameter D can be obtained by changing to the second voltage and changing the collection state. It is possible to sufficiently discriminate the difference. Therefore, using this relationship, the average particle diameter D can be estimated and the number N of particles can be calculated.

As described above, the second voltage for changing the collection state of the particulate matter is higher or lower than the first voltage, and it is better that the potential difference is larger. However, if the voltage is high, the repulsive force is larger than the attractive force that attracts the particulate matter, so there is a risk that the particulate matter may peel off or discharge may occur. desirable. In addition, when the voltage is low, the strength of the electrostatic field between the electrodes becomes weak, so that the contact state is likely to change, and since the strength of the electrostatic field becomes zero at an applied voltage of 0 V, the effect of changing the contact state is most effective. growing.

The detection voltage for measuring the interelectrode resistance R may be any voltage that can read the difference in the interelectrode resistance R depending on the particle diameter, and a higher voltage is easier to read. In particular, when estimating the average particle diameter D and calculating the number N of particles with a minute amount of particulate matter, a high voltage is better because the difference in resistance between electrodes due to the particle diameter is not clear at low voltage. However, the second voltage and the detection voltage may be the same as long as the difference between the electrode resistances R due to the particle size can be read because it is necessary to suppress the voltage so that the separation of the particulate matter and the discharge do not occur. In addition, since the change in the interelectrode resistance R includes an irreversible change, if the second voltage that changes the collection state of the particulate matter is sandwiched, the detection is performed by measuring the first voltage that is the collection voltage and the interelectrode resistance. The working voltage may be the same.

As shown in the above embodiments, a voltage is applied to the detection unit 2 of the particulate matter detection sensor 1 to collect the particulate matter, and the applied voltage is changed to measure the interelectrode resistance R. By providing a sensor control unit that calculates the number of particles of the particulate matter, the number of particles of the particulate matter can be accurately detected. Further, such a particulate matter detection device can be used for an exhaust gas purification device of an internal combustion engine or the like to perform a failure diagnosis of the DPF 5 disposed upstream.

In each of the above embodiments, the average particle diameter of the particulate matter is estimated from the resistance value obtained by changing the voltage. However, the particulate matter is obtained using the resistance value obtained by changing the current. The average particle diameter D may be estimated. That is, the first current is applied to the detection unit 2 of the particulate matter detection sensor 1 to collect the particulate matter, and the applied current is different from the first current in a state where the sensor output reaches the threshold value. Alternatively, the interelectrode resistance R in the detection unit 2 may be detected.

Moreover, in the said embodiment, although the threshold value was set to the predetermined output value V0 used as the detection reference in the collection control part 41, it is not restricted to this, The sensor output V which can detect a particulate matter is used. Based on this, it can be set arbitrarily.
Alternatively, the value is not limited to the sensor output V, and may be any value that serves as a reference indicating that particulate matter can be detected. For example, an elapsed time from when electrostatic collection is started by applying a first voltage in the collection control unit 41 until detection of particulate matter is possible (for example, detection time t in FIG. 4). A threshold can also be set based on
The sensor output may be an output voltage or an output current.

The particulate matter detection device of the present disclosure including the particulate matter detection sensor 1 and the ECU 4 is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the present disclosure. For example, in the first embodiment, the protective cover 12 that covers the sensor element 10 of the particulate matter detection sensor 1 has a single cylinder structure, but a double cylinder structure including an inner cylinder and an outer cylinder may be used. The arrangement and number of the gas flow holes 13 and 14 to be measured provided in the protective cover 12 can also be set arbitrarily. In addition, the shape and material of each part of the sensor element 10 and the protective cover 12 constituting the particulate matter detection sensor 1 can be appropriately changed.

In the first embodiment, the internal combustion engine E is a diesel engine and the DPF 5 serving as a particulate matter collection unit is disposed. However, a gasoline particulate filter may be disposed using the internal combustion engine E as a gasoline engine. Further, the present invention is not limited to the combustion exhaust gas of the internal combustion engine E, and can be applied to any gas to be measured as long as it includes a particulate matter.

The present disclosure is not limited to the above embodiments, and can be applied to various embodiments without departing from the scope of the disclosure.

Claims (22)

1. A particulate matter detection device for detecting particulate matter contained in a gas to be measured,
   Particulate matter which is electrostatically collected by the detection unit (2) having a detection unit (2) in which a pair of spaced apart electrodes (21, 22) are arranged on the surface of the substrate (11) exposed to the gas to be measured A sensor unit (1) for outputting a signal corresponding to the amount of
   A sensor control unit (4) for detecting the number (N) of particulate matter electrostatically collected by the detection unit based on a sensor output (V) transmitted from the sensor unit. ,
   The sensor control unit
   A collection control unit (41) that applies a first voltage between the pair of electrodes of the detection unit and electrostatically collects particulate matter in the detection unit;
   The resistance value (R) between the pair of electrodes is changed after changing the applied voltage between the pair of electrodes to a second voltage different from the first voltage in a state where the sensor output at the first voltage has reached a threshold value. ) And the number of particles calculated from the average particle diameter (D) of the particulate matter estimated from the resistance value and the mass (M) of the particulate matter estimated from the sensor output A particulate matter detection device comprising: a number calculation unit (42).
2. The particle number calculation unit
   When the sensor output at the first voltage for electrostatic collection reaches the threshold, the voltage applied between the pair of electrodes is changed to the second for changing the collection state of the particulate matter. A voltage control unit (421) for controlling to a detection voltage for detecting the resistance between the electrodes, which is the same voltage as or different from the second voltage after changing to the voltage;
   The particulate matter detection device according to claim 1, further comprising: an interelectrode resistance detection unit (422) that detects a resistance value (R) between the pair of electrodes in the detection voltage.
3. A particulate matter detection device for detecting particulate matter contained in a gas to be measured,
   Particulate matter which is electrostatically collected by the detection unit (2) having a detection unit (2) in which a pair of spaced apart electrodes (21, 22) are arranged on the surface of the substrate (11) exposed to the gas to be measured A sensor unit (1) for outputting a signal corresponding to the amount of
   A sensor control unit (4) for detecting the number (N) of particulate matter electrostatically collected by the detection unit based on a sensor output (V) transmitted from the sensor unit. ,
   The sensor control unit
   A collection control unit (41) that applies a first voltage between the pair of electrodes of the detection unit and electrostatically collects particulate matter in the detection unit;
   In a state where the sensor output at the first voltage reaches a threshold value, the voltage applied between the pair of electrodes is changed to a second voltage different from the first voltage, and then the pair at a plurality of voltages having different magnitudes. The resistance values (R, R1) between the electrodes are detected, and the average particle diameter (D) of the particulate matter estimated from the resistance value and the mass (M) of the particulate matter estimated from the sensor output are obtained. And a particle number calculation unit (42) for calculating the number of particles.
4. The particle number calculation unit
   When the sensor output at the first voltage for electrostatic collection reaches the threshold, the voltage applied between the pair of electrodes is changed to the second for changing the collection state of the particulate matter. A voltage control unit (421) that sequentially controls the plurality of voltages to be detection voltages for detecting the interelectrode resistance after changing to the voltage;
   The particulate matter detection device according to claim 3, further comprising: an inter-electrode resistance detection unit (422) that detects resistance values between the pair of electrodes at the plurality of voltages.
5. The particulate matter detection device according to claim 3 or 4, wherein the particle number calculation unit weights each of the resistance values detected at the plurality of voltages to estimate the average particle diameter.
6. A particulate matter detection device for detecting particulate matter contained in a gas to be measured,
   Particulate matter which is electrostatically collected by the detection unit (2) having a detection unit (2) in which a pair of spaced apart electrodes (21, 22) are arranged on the surface of the substrate (11) exposed to the gas to be measured A sensor unit (1) for outputting a signal corresponding to the amount of
   A sensor control unit (4) for detecting the number (N) of particulate matter electrostatically collected by the detection unit based on a sensor output (V) transmitted from the sensor unit. ,
   The sensor control unit
   A collection control unit (41) that applies a first voltage between the pair of electrodes of the detection unit and electrostatically collects particulate matter in the detection unit;
   In a state where the sensor output at the first voltage reaches a threshold value, the voltage applied between the pair of electrodes is changed to a second voltage different from the first voltage, and then the pair at a plurality of voltages having different magnitudes. The resistance values (R, R1) between the electrodes are detected and estimated from the average particle diameter (D) of the particulate matter estimated from the slope in the relationship between the plurality of voltages and the resistance value, and the sensor output. A particulate matter detection device comprising: a particle number calculation unit (42) that calculates the number of particles using a mass (M) of the particulate matter.
7. The particle number calculation unit
   When the sensor output at the first voltage for electrostatic collection reaches the threshold, the voltage applied between the pair of electrodes is changed to the second for changing the collection state of the particulate matter. A voltage control unit (421) that sequentially controls the plurality of voltages to be detection voltages for detecting the interelectrode resistance after changing to the voltage;
   An inter-electrode resistance detection unit (422) that detects a resistance value between the pair of electrodes at the plurality of voltages, and an inclination calculation unit that calculates an inclination in a relationship between the plurality of voltages and the resistance value. The particulate matter detection device according to claim 6.
8. The particulate matter detection device according to any one of claims 3 to 7, wherein the plurality of voltages include a voltage having the same magnitude as the second voltage.
9. A particulate matter detection device for detecting particulate matter contained in a gas to be measured,
   Particulate matter which is electrostatically collected by the detection unit (2) having a detection unit (2) in which a pair of spaced apart electrodes (21, 22) are arranged on the surface of the substrate (11) exposed to the gas to be measured A sensor unit (1) for outputting a signal corresponding to the amount of
   A sensor control unit (4) for detecting the number (N) of particulate matter electrostatically collected by the detection unit based on a sensor output (V) transmitted from the sensor unit. ,
   The sensor control unit
   A collection control unit (41) that applies a first current between the pair of electrodes of the detection unit and electrostatically collects particulate matter in the detection unit;
   The resistance value (R) between the pair of electrodes is changed after the applied current between the pair of electrodes is changed to a second current different from the first current in a state where the sensor output at the first current has reached a threshold value. ) And the number of particles calculated from the average particle diameter (D) of the particulate matter estimated from the resistance value and the mass (M) of the particulate matter estimated from the sensor output A particulate matter detection device comprising: a number calculation unit (42).
10. The threshold is set based on the sensor output at which the particulate matter can be detected in the collection control unit or the elapsed time from the start of electrostatic collection until the particulate matter can be detected. The particulate matter detection device according to any one of claims 1 to 9, wherein:
11. The threshold value is an output value (V0) serving as a particulate matter detection reference in the collection control unit,
    The particulate matter detection device according to any one of claims 1 to 10, wherein the particle number calculation unit calculates the mass of the particulate matter using an output value serving as the detection reference.
12. The sensor part has a heater part (3) provided with a heater electrode (31) for heating the detection part,
    The sensor control unit includes a heating control unit (43) that supplies electric power to the heater unit and heats and maintains the SOF in the particulate matter at a temperature at which the SOF can volatilize and the soot does not burn. The particulate matter detection device according to any one of claims 1 to 11.
13. The particulate matter detection device according to claim 12, wherein the temperature is 200 ° C or higher and 400 ° C or lower.
14. The threshold value is an output value (V0) serving as a particulate matter detection reference in the collection control unit,
    The particle number calculation unit calculates the mass of the particulate matter using an output value serving as the detection reference or a first output value (V1) that is the sensor output during heating holding by the heating control unit. The particulate matter detection device according to claim 12 or 13.
15. The particle number calculation unit calculates the number of particles from the mass of the particulate matter, the average particle diameter of the particulate matter, and the specific gravity of the particulate matter. The particulate matter detection device according to 1.
16. The particulate matter according to claim 15, wherein the specific gravity of the particulate matter is a constant value or a value estimated based on an average particle diameter of the particulate matter estimated by the particle number calculation unit. Substance detection device.
17. The particulate matter detection device according to any one of claims 1 to 16, wherein the substrate is made of an insulating material.
18. The detection unit has a pair of electrodes spaced from each other on the surface of the detection conductive part opposite to the base, the detection conductive part (23) being disposed on the surface of the base. The particulate matter detection device according to any one of 17.
19. The particulate matter detection device according to claim 18, wherein the detection conductive part is made of a conductive material having an electrical resistivity higher than that of the particulate matter.
20. The detection conductive part is made of a conductive material having a surface electrical resistivity ρ of 1.0 × 10 ⁷ to 1.0 × 10 ¹⁰ Ω · cm in a temperature range of 100 to 500 ° C. 19. The particulate matter detection device according to 19.
21. The conductive material is a ceramic having a perovskite structure whose molecular formula is represented by ABO ₃ , the A site in the molecular formula is at least one selected from La, Sr, Ca, and Mg, and the B site is Ti 21. The particulate matter detection device according to claim 20, wherein the particulate matter detection device is at least one selected from Al, Zr, and Y.
22. 22. The particulate matter detection device according to claim 21, wherein the A site has Sr as a main component and La as a subcomponent, and the B site is Ti.

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